Orreries for displaying planetary bodies such as planets of the solar system or their moons, are well known. Such orreries typically consist of planetary body representations mounted on the end of an arm, the opposite end of the arm being either rotatably mounted on a shaft or fixedly mounted to a shaft which itself can be rotated. Generally, the latter method is used and when a plurality of planetary body representations are to be displayed, the shafts are mounted, concentrically. These shafts are then driven usually through gear trains from a single drive source such as a hand crank or electric motor. Often it is desirable to rotate the planetary body representations at their correct relative rotational velocities which for orreries of the latter type resulted in relatively complex gear trains. These gear trains when combined with the remainder of the orrery mechanism, often produced an orrery which was bulky and mechanically complex and which was not readily capable of assembly and disassembly when desired.